diff --git a/core/tests/coretests/src/com/android/internal/util/HexDumpTest.java b/core/tests/coretests/src/com/android/internal/util/HexDumpTest.java
index 359bd5e93daeb..4f0becc8ad5d8 100644
--- a/core/tests/coretests/src/com/android/internal/util/HexDumpTest.java
+++ b/core/tests/coretests/src/com/android/internal/util/HexDumpTest.java
@@ -16,8 +16,16 @@
 
 package com.android.internal.util;
 
+import static com.android.internal.util.HexDump.hexStringToByteArray;
+import static com.android.internal.util.HexDump.toHexString;
+
 import junit.framework.TestCase;
 
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.util.Arrays;
+import java.util.Random;
+
 public final class HexDumpTest extends TestCase {
     public void testBytesToHexString() {
         assertEquals("abcdef", HexDump.toHexString(
@@ -25,7 +33,142 @@ public final class HexDumpTest extends TestCase {
         assertEquals("ABCDEF", HexDump.toHexString(
                 new byte[] { (byte) 0xab, (byte) 0xcd, (byte) 0xef }, true));
     }
-    public void testNullArray() {
-        assertEquals("(null)", HexDump.toHexString(null));
+
+    public void testNullByteArray() {
+        assertThrows(
+                NullPointerException.class,
+                () -> HexDump.toHexString(null));
     }
+
+    public void testBytesToHexString_allByteValues() {
+        byte[] bytes = new byte[256];
+        for (int i = 0; i < bytes.length; i++) {
+            bytes[i] = (byte) (i % 256);
+        }
+
+        StringBuilder sb = new StringBuilder();
+        for (char firstChar : "0123456789ABCDEF".toCharArray()) {
+            for (char secondChar : "0123456789ABCDEF".toCharArray()) {
+                sb.append(firstChar).append(secondChar);
+            }
+        }
+        String expected = sb.toString();
+
+        assertEquals(expected, HexDump.toHexString(bytes));
+    }
+
+    public void testRoundTrip_fromBytes() {
+        Random deterministicRandom = new Random(31337); // arbitrary but deterministic
+        for (int length = 0; length < 100; length++) {
+            byte[] bytes = new byte[length];
+            deterministicRandom.nextBytes(bytes);
+            byte[] reconstruction = hexStringToByteArray(toHexString(bytes));
+
+            assertBytesEqual(bytes, reconstruction);
+        }
+    }
+
+    public void testRoundTrip_fromString() {
+        String hexString = "0123456789ABCDEF72f9a3438934c378d34f32a8b932";
+        for (int length = 0; length < hexString.length(); length += 2) {
+            String original = hexString.substring(0, length);
+            String reconstruction = toHexString(hexStringToByteArray(original));
+            assertEquals(original.toUpperCase(), reconstruction);
+        }
+    }
+
+    public void testToHexString_offsetLength() {
+        byte[] bytes = new byte[32];
+        for (int i = 0; i < 16; i++) {
+            bytes[i] = (byte) i;
+            bytes[16 + i] = (byte) (16 * i);
+        }
+        String expected = "000102030405060708090A0B0C0D0E0F00102030405060708090A0B0C0D0E0F0";
+        for (int offset = 0; offset < bytes.length; offset++) {
+            for (int len = 0; len < (bytes.length - offset); len++) {
+
+                byte[] subBytes = new byte[len];
+                System.arraycopy(bytes, offset, subBytes, 0, len);
+
+                String actual = toHexString(bytes, offset, len);
+                assertEquals(expected.substring(2 * offset, 2 * offset + 2 * len), actual);
+                assertEquals(toHexString(subBytes), actual);
+            }
+        }
+    }
+
+    public void testToHexString_case() {
+        byte[] bytes = new byte[32];
+        for (int i = 0; i < 16; i++) {
+            bytes[i] = (byte) i;
+            bytes[16 + i] = (byte) (16 * i);
+        }
+
+        String expected = "000102030405060708090A0B0C0D0E0F00102030405060708090A0B0C0D0E0F0";
+
+        assertEquals(expected.toUpperCase(), toHexString(bytes, true));
+        assertEquals(expected.toLowerCase(), toHexString(bytes, false));
+
+        // default is uppercase
+        assertEquals(expected.toUpperCase(), toHexString(bytes));
+    }
+
+    public void testHexStringToByteArray_empty() {
+        assertBytesEqual(new byte[0], HexDump.hexStringToByteArray(""));
+    }
+
+    public void testHexStringToByteArray_null() {
+        assertThrows(
+                NullPointerException.class,
+                () -> HexDump.hexStringToByteArray((String) null));
+    }
+
+    public void testHexStringToByteArray_invalidCharacters() {
+        // IllegalArgumentException would probably have been better than RuntimeException, but it
+        // might be too late to change now.
+        assertThrows(
+                RuntimeException.class,
+                () -> HexDump.hexStringToByteArray("GG"));
+        assertThrows(
+                RuntimeException.class,
+                () -> HexDump.hexStringToByteArray("\0\0"));
+        assertThrows(
+                RuntimeException.class,
+                () -> HexDump.hexStringToByteArray("abcdefgh"));
+    }
+
+    public void testHexStringToByteArray_oddLength() {
+        // IllegalArgumentException would probably have been better than
+        // StringIndexOutOfBoundsException, but it might be too late to change now.
+        assertThrows(
+                StringIndexOutOfBoundsException.class,
+                () -> HexDump.hexStringToByteArray("A"));
+        assertThrows(
+                StringIndexOutOfBoundsException.class,
+                () -> HexDump.hexStringToByteArray("123"));
+        assertThrows(
+                StringIndexOutOfBoundsException.class,
+                () -> HexDump.hexStringToByteArray("ABCDE"));
+    }
+
+    private static void assertBytesEqual(byte[] expected, byte[] actual) {
+        if (!Arrays.equals(expected, actual)) {
+            fail("Expected " + Arrays.toString(expected) + ", got " + Arrays.toString(actual));
+        }
+    }
+
+    private static void assertThrows(Class<? extends RuntimeException> clazz, Runnable runnable) {
+        try {
+            runnable.run();
+        } catch (RuntimeException exception) {
+            assertEquals(toStrackTrace(exception), clazz, exception.getClass());
+        }
+    }
+
+    private static String toStrackTrace(Throwable throwable) {
+        StringWriter stringWriter = new StringWriter();
+        throwable.printStackTrace(new PrintWriter(stringWriter));
+        return stringWriter.toString();
+    }
+
 }